Aircraft provided with a buoyancy system, and a buoyancy method

ABSTRACT

A buoyancy method for deploying a plurality of floats of a buoyancy system of an aircraft. The plurality of floats comprises a plurality of main floats and a plurality of secondary floats that are folded in flight. The method comprises a step of deploying the main floats in flight prior to ditching, and a step of deploying the secondary floats after ditching.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to French patent application No. FR1770571 filed on Jun. 2, 2017, the disclosure of which is incorporatedin its entirety by reference herein.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to an aircraft provided with a buoyancysystem, and it also relates to a buoyancy method.

2) Description of Related Art

Under such circumstances, the invention lies in the technical field ofbuoyancy systems for aircraft, and more particularly for a rotary wingaircraft.

Such a buoyancy system contributes to enabling an aircraft to float instable manner after ditching in water. By way of example, the buoyancysystem may be used following forced ditching in order to enable theoccupants of the aircraft to evacuate it. Aircraft that performsmissions of transporting people off-shore are in principle fitted withsuch buoyancy systems.

Certification regulations also specify that an aircraft must be capableof ditching and floating in stable manner on the water with its buoyancysystem. Stability must be effective for certain states of the freesurface of the water and for certain wind levels that are defined inthose certification regulations.

Those states of the free surface of the water are also referred to as“sea states”, and they apply to any liquid surface. The term “ditching”covers an aircraft landing on any free water surface, whether it be thesea or on a lake, for example. Certification regulations require anaircraft to be stable with a particular sea state.

A buoyancy system may include floats.

The floats are fastened on either side of an airframe of the aircraft.The term “airframe” is used in particular to designate a portion of theaircraft housing a cockpit, and possibly also a cabin and a hold, andpossibly including landing gear. On a helicopter, the airframe carriesthe main rotor of the helicopter. By way of example, floats may befastened to landing gear of the airframe, or else to a wall of theairframe.

Furthermore, the floats may for example be folded under normal flyingconditions, and then deployed in the event of ditching. By way ofillustration, a float may comprise an inflatable bag that can beattached to an airframe by means of at least one cord.

A buoyancy system comprising folded floats then includes deploymentmeans for deploying the floats, e.g. an inflater. Certain buoyancysystems include deployment means that are deployed under the control ofthe pilot and/or the copilot, for example, and/or under the control ofan automatic trigger device. For example, a button may be located on astick operated by a pilot, the button being connected to an inflater.Operating the button then causes the float to inflate.

In addition, in a first strategy, the floats may be deployed afterditching.

This first strategy makes it possible to avoid subjecting the floats tothe forces that result from ditching. This makes the floats and thecords easier to design. Furthermore, the means for deploying the floatsmay include immersion sensors for detecting the presence of water inorder to activate deployment of the floats without involving a pilot.

In contrast, the buoyancy of the aircraft is not optimized until thefloats have been deployed.

In a second strategy, the floats may be deployed in flight, i.e. beforethe aircraft touches the water. When a pilot or a system detects thatditching is about to take place, the pilot or the system causes thefloats to be deployed. This second strategy is advantageous in that itensures that buoyancy of the aircraft is optimized even before theaircraft is on the water. The depth to which the aircraft goes down intothe water on ditching can then be minimized. Furthermore, the floatsabsorb a portion of the force to which the aircraft is subjected duringditching.

Nevertheless, under such circumstances, the buoyancy system needs to bedesigned to withstand the forces that result from the impact of theaircraft on the water. The floats may also tend to move considerably asa result of coming into contact with the water and they run the risk ofstriking against surfaces of the aircraft. This can lead to suchsurfaces being pushed in.

Optionally, the aircraft may include in parallel an emergency system fordeploying the floats after ditching.

The second strategy is sometimes preferred in order to optimize thebuoyancy of an aircraft because of its ability to tend to stabilize theaircraft as soon as it touches the water, since the floats are deployedin flight. Nevertheless, designing such a buoyancy system for applyingthis second strategy can be difficult.

In this context, document FR 3 047 231 describes a method of authorizinginflation of floats in flight under predetermined conditions that tendto limit the impacts of such inflation.

Document EP 1 429 958 is remote from this problem in that it describes abuoyancy system having at least one inflatable float and an inflatableraft.

Documents FR 3 043 061, US 2003/060101, FR 2 997 923, DE 1 213 255, andUS 2014/252165 are also known.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is thus to propose a method and anaircraft including a novel buoyancy system.

The invention thus provides a buoyancy method for deploying a pluralityof floats of a buoyancy system of an aircraft.

The plurality of floats comprises a plurality of main floats and aplurality of secondary floats, said main floats and said secondaryfloats being folded in flight and being for deploying outside anairframe of the aircraft in order to stabilize said aircraft on a liquidsurface, the method comprising the following steps:

deploying said main floats in flight prior to ditching, namely beforethe aircraft reaches a liquid surface; and

deploying said secondary floats after ditching.

The term “outside an airframe” means that the floats are not arrangedwithin a cabin, but are situated on the outside of the aircraft oncethey are deployed.

Such a method tends to combine the advantages of the above-mentionedfirst and second strategies.

Specifically, the method provides for deploying floats sequentially.

When the crew or calculation means of the aircraft detect that ditchingis imminent, only the main floats are deployed in flight. The mainfloats contribute to stabilizing the aircraft on the liquid surface atthe moment of impact on that liquid surface. After ditching, thesecondary floats are deployed in turn in order to increase the stabilityof the aircraft.

Because of the presence of the secondary floats, the main floats may beof smaller dimensions than the floats in the prior art. For example, aprior art float is replaced by both a main float and also a secondaryfloat, the main float and the secondary float together presenting avolume that is substantially equal to the volume of the prior art float,or possibly even a smaller volume given an increased spread of thefloat. Under such circumstances, the main floats are subjected to forcesthat are smaller than the forces to which prior art floats aresubjected.

Compared with a buoyancy system applying the first strategy of the priorart, this method tends to reduce the loads exerted on the floats and theassociated fastener devices during ditching. This can result in a weightsavings.

In addition, the method tends to reduce the risk of the floats beingpunctured on coming into contact with the liquid surface.

Furthermore, because of the presence of the secondary floats, theconsequences of a main float bursting on ditching can be minimized.Likewise, the consequences of an accidental puncture can be reduced.

In another aspect, the secondary floats may be spaced apart by a largespread, which spread tends to improve the stability of the aircraft.

The freedom of movement of the floats is possibly also limited.

Compared with a buoyancy system making use of the second strategy of theprior art, this method tends to improve the stability of the aircraftduring ditching, and tends to limit the depth to which the aircraft goesdown into the water.

In addition, the main floats tend to reduce the load that needs to beabsorbed by the airframe on impact with the liquid surface.

The method may also include one or more of the followingcharacteristics.

Thus, the method may include a step of pairing said floats, saidplurality of floats comprising at least one pair of main floats and atleast one pair of secondary floats, each of said at least one pair ofmain floats comprising two main floats arranged transversely on eitherside of said airframe, and each of said at least one pair of secondaryfloats comprising two secondary floats arranged transversely on eitherside of said airframe.

The floats are paired in order to optimize the stability of theaircraft.

In an aspect, the method may include a step of forming a plurality offloat units, each float unit comprising a single main float and a singlesecondary float arranged side by side, each main float of a float unitbeing arranged transversely between the secondary float of said floatunit and said airframe of the aircraft.

The aircraft then has float units, each comprising a secondary floatarranged beside or indeed against a main float. A float unit tends toform a float having two compartments.

The secondary float of a float unit may be secured to the main float ofthat float unit. In one variant, the secondary float of a float unit isstitched and/or adhesively bonded to the main float of the float unit.In another variant, the secondary float and the main float of a floatunit present a common partition, thereby forming a singlecompartmentalized balloon.

In addition, a secondary float of a float unit is spaced apart from theairframe by the main float of the float unit. This configuration tendsto maximize the transverse distance between two secondary floats andthus to improve the floating stability of the aircraft. Because of thisarrangement, the main floats may be referred to as “inner” floats andthe secondary floats may be referred to as “outer” floats. Furthermore,the volumes of the main and secondary floats, once deployed, mayoptionally be minimized.

The invention also provides an aircraft having a buoyancy system, saidbuoyancy system comprising a plurality of floats, each float of saidplurality of floats being folded in flight other than during a stage ofditching, said buoyancy system including a deployment system fordeploying each float of said plurality of floats outside an airframe ofthe aircraft.

Said plurality of floats comprises a plurality of main floats and aplurality of secondary floats, said buoyancy system being configured todeploy said main floats outside said airframe in flight prior toditching and to deploy said secondary floats outside said airframe afterditching.

The aircraft may also include one or more of the followingcharacteristics.

Thus, the plurality of floats may form a plurality of float units, eachfloat unit having a single main float and a single secondary floatarranged side by side, a main float of a float unit being arrangedtransversely between the secondary float of said float unit and saidairframe.

For example, each float unit may be arranged to take the place of aprior art float.

Optionally, said plurality of float units comprises at least one pair offloat units, said at least one pair of float units comprising two floatunits arranged transversely on either side of said airframe.

For example, the aircraft may have an even number of float units, thefloat units also being paired.

By way of illustration, the aircraft may have a front pair of floatunits comprising a left front float unit and a right front float unit.The aircraft may have a rear pair of float units comprising a left rearfloat unit and a right rear float unit. The terms “front” and “rear”should be considered relative to the direction of advance of theaircraft towards the front.

In an aspect, said two float units of a pair of float units are arrangedsymmetrically on either side of said airframe.

For example, the two float units of a pair of float units may bearranged symmetrically on either side of an anteroposterior plane ofsymmetry of the aircraft.

In an aspect, a secondary float and a main float may have a partition incommon.

In an aspect, a secondary float is stitched and/or adhesively bonded toa main float.

The term “and/or” means that either a secondary float is stitched to amain float, or that a secondary float is adhesively bonded to a mainfloat, or indeed that a secondary float is both stitched and adhesivelybonded to a main float.

In an aspect, each main float is connected to the airframe by at leastone main cord.

Thus, a main float is locally attached to the airframe of the aircraft,but it can move relative to the airframe. Furthermore, such a cord seeksto limit the freedom of movement of the main float.

In an aspect, each secondary float is connected to the airframe by atleast one secondary cord.

Optionally, each secondary float is also secured to a main float, eitherby presenting a partition in common with the main float or else by beingadhesively bonded and/or stitched to the main float.

The secondary floats may have cords specific thereto in order tooptimize the stability of the aircraft.

In a first embodiment, the deployment system may comprise at least onemain inflater in fluid flow communication with only at least one mainfloat to deploy only the at least one main floats, said deploymentsystem including at least one secondary inflater in fluid flowcommunication with only at least one secondary float in order to inflateonly the at least one secondary floats.

The term “with only at least one main float” means that a main inflatercannot be directly connected to a secondary float. A main inflaterinjects fluid into one or more main floats. Likewise, the term “withonly at least one secondary float” means that a secondary inflatercannot be connected directly to a main float.

The term “inflater” designates any system serving to inflate at leastone float, i.e. enabling it to be unfolded so as to make it operational.Thus, the inflater may be a device that injects fluid into a float orthat deform a float. By way of example, the inflater may be an inflaterthat is electrical, explosive, or chemical.

The deployment system may include various inflaters respectivelyassociated with deploying the main floats and the secondary floats.

The main floats and the secondary floats are independent, the deploymentof the main floats not leading to the deployment of the secondaryfloats, and vice versa.

In a second embodiment, each secondary float is in fluid flowcommunication with at least one main float via a valve, said deploymentsystem comprising at least one main inflater in fluid flow communicationwith only the main floats in order to inject a fluid only into the mainfloats, no inflater directly feeding any secondary float with fluid.

Prior to ditching, each main inflater injects fluid into at least onemain float in order to inflate it. Each main float thus presents a firstvolume V1, with a first pressure P1 existing inside the main float.

The valves are also closed. Under such circumstances, the secondaryfloats are not deployed.

At the moment of the aircraft impacting against a liquid surface, orpossibly as a result of the impact, the valves are open.

The secondary floats are then inflated using the fluid contained in themain floats. At equilibrium, the main floats and the secondary floatsare inflated.

In a first variant of the second embodiment, said valve is a passivevalve, said passive valve opening when pressure existing in said mainfloat provided with the passive valve exceeds a threshold, said pressurebeing less than said threshold prior to ditching.

Such a passive valve may be in the form of a pressure release valve, aball valve, . . . .

In a second variant of the second embodiment, said aircraft includes aprocessor unit, said valve is an active valve, said active valve isconnected to said processor unit, and said active valve is controlled bysaid processor unit.

By way of example, an active valve may be an electromechanical valvecontrolled by a processor unit so as to open it or close it.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages appear in greater detail from thecontext of the following description of examples given by way ofillustration and with reference to the accompanying figures, in which:

FIG. 1 is a diagram showing an aircraft of the invention having mainfloats and secondary floats that are folded in forward flight and thatare not in fluid flow communication;

FIG. 2 is a diagram showing a main float in fluid flow communicationwith a secondary float;

FIG. 3 is a diagram showing a step of deploying main floats in flightprior to ditching;

FIG. 4 is a diagram showing a step of deploying secondary floats afterditching; and

FIG. 5 is a diagram showing an aircraft having a plurality of floatunits.

DETAILED DESCRIPTION OF THE INVENTION

Elements present in more than one of the figures are given the samereferences in each of them.

Three mutually orthogonal directions X, Y, and Z are shown in some ofthe figures.

The first direction X is said to be longitudinal. The term“longitudinal” relates to any direction parallel to the first directionX.

The second direction Y is said to be transverse. The term “transverse”relates to any direction parallel to the second direction Y.

Finally, the third direction Z is said to be in elevation. The term “inelevation” relates to any direction parallel to the third direction Z.

FIG. 1 shows an aircraft 1 having a buoyancy system 20 of the invention.The aircraft may for example be a rotorcraft.

The aircraft 1 has an airframe 2. The airframe 2 extends longitudinallyfrom a front end 4 to a rear end 3 along an anteroposterior plane 100.In addition, the airframe 2 extends transversely from a left flank 7 toa right flank 8 on either side of the anteroposterior plane 100, and itextends in elevation from a bottom portion 5 to a top portion 6.Optionally, the anteroposterior plane is a plane of symmetry of theaircraft. The terms “left” and “right” are defined as seen by anindividual located in the airframe and looking forwards towards thefront of the aircraft.

The bottom portion 5 includes a bottom of the airframe 2, while the topportion 6 includes a top of the airframe 2. The bottom portion 5 isconventionally provided with landing gear 95, whereas the top portionmay carry a rotor 9 that contributes to providing the aircraft with liftand possibly also propulsion. The rotor 9 is driven in rotation by apower plant 10. The power plant 10 includes at least one engine 11 andat least one main power transmission gearbox (MGB) 12 interposed betweenthe engine 11 and the rotor 9.

The airframe may carry other rotors, e.g. a tail rotor contributing tocontrolling yaw movement of the rotorcraft.

In addition, the aircraft 1 is also provided with a buoyancy system 20of the invention in order to enable it to ditch on water.

Such a buoyancy system 20 is provided with a plurality of floats 25, 30.Each float may comprise an envelope 26, 31 that floats on water, theenvelope holding captive a gas, for example.

Each float 25, 30 may be attached via its envelope and/or by means of atleast one cord 80, 85 to a structure of the airframe 2, specifically byway of example to a wall 13 of the airframe 2 or to an undercarriage, .. . . By way of example, the floats 25, 30 are connected to a lowportion of the aircraft situated in the proximity of, or indeed levelwith, the bottom of the airframe. Where appropriate, the floats 25, 30may be connected to a skid undercarriage.

In particular, the buoyancy system 20 is provided with at least two“main” floats 25. Each main float 25 is located on the outside EXT ofthe airframe 2. The term “located on the outside EXT of the airframe 2”means that the floats in question are deployed at least in part outsidethe airframe 2 in order to enable the aircraft to float. The main floats25 may be fastened in conventional manner to a wall 13 of the airframe 2and/or to an undercarriage, for example, by means of at least one maincord 80 connecting an envelope 26 of a main float to the airframe and/orby means of the envelope 26 of a main float being fastened to theairframe.

The main floats may be paired. Thus, one pair 27 of main floats 25comprises a left main float that is arranged beside the left flank 7 ofthe aircraft, and a right main float that is arranged beside the rightflank 8 of the aircraft. The two main floats 25 of a pair may bearranged symmetrically on either side of the anteroposterior plane 100of symmetry of the aircraft, when the aircraft is in a stable position.

For example, the aircraft may have one or indeed two pairs 27 of mainfloats 25.

With reference to FIG. 2, the buoyancy system 20 also has at least two“secondary” floats 30. Each secondary float 30 is arranged on theoutside EXT of the airframe 2.

The secondary floats 30 may be paired. Thus, one pair 32 of secondaryfloats 30 comprises a left secondary float that is arranged beside theleft flank 7 of the aircraft, and a right secondary float that isarranged beside the right flank 8 of the aircraft. The two secondaryfloats 30 of a pair may be arranged symmetrically on either side of theanteroposterior plane 100 of symmetry of the aircraft when the aircraftis in a stable position.

The secondary floats 30 may be fastened in conventional manner to a wall13 of the airframe 2 and/or to an undercarriage, for example, by meansof at least one secondary cord 85 connecting an envelope 31 of asecondary float to the airframe and/or by fastening the envelope 31 of asecondary float to the airframe.

In addition, or as an alternative, each secondary float 30 may befastened to a main float 25. For example, an envelope 26 of a main float25 may be stitched and/or adhesively bonded to an envelope 31 of asecondary float 30. In another example, a main float 25 and a secondaryfloat 30 may have a partition 29 in common. The term “partition”designates a portion of the envelope 31 of a secondary float that alsoconstitutes a portion of the envelope 26 of a main float.

A main float 25 may also be arranged transversely between a secondaryfloat 30 and the anteroposterior plane 100 and/or the airframe 2.

Furthermore, the main floats 25 and the secondary floats 30 may formfloat units 35.

Such a float unit 35 comprises a main float 25 and a secondary float 30that are arranged beside each other, and by way of example transversely,one beside the other in a direction perpendicular to the anteroposteriorplane 100. Within a float unit, the main float 25 is arrangedtransversely between the secondary float 30 and the anteroposteriorplane 100 and/or the airframe 2.

By way of example, the aircraft may have its floats in float units 35only. The aircraft then does not have a main float 25 or a secondaryfloat 30 that is isolated, i.e. not forming part of a float unit 35. Theaircraft is provided with float units 35 only, each comprising a mainfloat 25 and a secondary float 30.

Optionally, the aircraft includes at least one pair 39 of float units.Such a pair 39 of float units is provided with two float units arrangedtransversely on either side of the airframe 2 and of the anteroposteriorplane 100 in a direction that is perpendicular to the anteroposteriorplane 100, for example. Thus, a pair 39 of float units includes a leftfloat unit 37 situated on the left side 7 of the aircraft and a rightfloat unit 38 situated on the right side 8 of the aircraft.

Optionally, the aircraft has an even number of float units, all of thefloat units also being paired so that each of them belongs to a pair 39of float units.

In an aspect, two float units 37, 38 in a pair 39 of float units arearranged symmetrically on either side of the airframe 2 and/or of theanteroposterior plane 100.

Furthermore, the main floats 25 and the secondary floats 30 are foldedunder normal conditions, i.e. other than during a stage of ditching, inorder to reduce their overall size.

For example, the main floats 25 and the secondary floats are folded andarranged in a conventional covering 75, which covering opens while thefloats are being deployed. Where appropriate, a single covering 75 maysurround both the main floats 25 and the secondary floats 30 of a floatunit 35.

In order to optimize the stability of an aircraft on a liquid surface,the main floats 25 and the secondary floats 30 are deployed in order tooccupy a large volume. For example, the main floats 25 and the secondaryfloats 30 may be inflatable floats, each of these inflatable floatspresenting an envelope that unfolds when a fluid is injected into theenvelope. Under such circumstances, the main floats 25 and the secondaryfloats 30 are deflated other than during stages of ditching, and theyare inflated in order to float on a liquid surface.

In order to deploy the floats, i.e. in order to unfold them, thebuoyancy system includes a deployment system 50 for deploying the mainfloats 25 and the secondary floats 30, i.e. for increasing the volumesof the main floats 25 and of the secondary floats 30. When thedeployment system 50 is activated, it serves to unfold the main floats25 and the secondary floats 30 in order to increase their volumes so asto stabilize the aircraft on a liquid surface.

Under such conditions, the deployment system 50 may include at least oneinflater referred to for convenience as a “main” inflater 51. Each maininflater is in fluid flow communication with at least one main float 25.

For example, a single main inflater 51 is connected to all of the mainfloats 25 via a plurality of pipes. In another example, the deploymentsystem has as many main inflaters as it has main floats, each main floatbeing connected by a pipe to an inflater that is dedicated thereto. Inanother example, two main inflaters may be connected via at least onepipe to the same main float 25. Naturally, other configurations arepossible, it being possible for a single main inflater to inflate one ormore main floats.

The deployment system may include a main control member 52 connected toeach main inflater in order to control the operation of each maininflater. The term “main control member” 52 designates a member that canbe operated by a pilot, such as for example: a button, a touch control,a voice control, a visual control, . . . .

The deployment system may include a main automatic control system 53that is connected to each main inflater in order to cause each maininflater to operate. The term “main automatic control system” 53designates a system that causes each main inflater to operate inapplication of predetermined logic, by generating a deployment orderautomatically when predetermined conditions are satisfied.

The main automatic control system 53 may include a calculator, e.g.possessing a processor, an integrated circuit, a programmable system, alogic circuit, these examples not limiting the scope to be given to theterm “calculator”. The calculator may optionally be engaged byactivation means operable by a person, for example a button. Theactivation means may possess at least one position enabling the mainautomatic control system 53 to be made active. Thus, the main automaticcontrol system 53 may be inhibited in certain situations, e.g. while theaircraft is not overlying a liquid surface.

By way of illustration, the calculator may be connected to altitudesensors in order to request operation of the main inflater when theaircraft reaches a threshold altitude, where applicable providing themain automatic control system 53 has been engaged.

The main automatic control system 53 and/or the main control member 52are configured to deploy the main floats in flight before ditching.

Reference may be made to the state of the art in order to findembodiments of inflaters and systems for controlling such inflaters todeploy the main floats in flight before ditching.

In the first embodiment of FIG. 1, the deployment system 50 may includeat least one inflater referred to for convenience as a “secondary”inflater 55. Each secondary inflater 55 is in fluid flow communicationwith at least one secondary float 30.

By way of example, a single secondary inflater 55 is connected to all ofthe secondary floats 30 via a plurality of pipes. In another example,the deployment system has as many secondary inflaters 55 as it hassecondary floats 30, each secondary float 30 being connected by a pipeto an inflater that is specific thereto. In another example, twosecondary inflaters 55 may be connected via at least one pipe to asingle secondary float 30. Other configurations are naturally possible,it being possible for a single secondary inflater to inflate one or moresecondary floats.

The deployment system may include a secondary control member 56connected to each secondary inflater to control the operation of eachsecondary inflater. The term “secondary control member” 56 designates amember that is operable by a pilot, e.g. a button, a touch control, avoice control, a visual control, . . . .

The deployment system may include a secondary automatic control system57 connected to each secondary inflater in order to cause each secondaryinflater to operate. The term “secondary automatic control system” 57designates a system that controls each secondary inflater in applicationof predetermined logic by generating a deployment order automaticallywhen predetermined conditions are satisfied. By way of illustration, asecondary automatic control system 57 is provided with calculation meansand with immersion sensors in order to cause the secondary inflater tooperate when the immersion sensors detect that the aircraft is immersed.

The secondary automatic control system 57 may include a calculatorreferred to as calculation means, e.g. possessing a processor, anintegrated circuit, a programmable system, a logic circuit, theseexamples not limiting the scope to be given to the term “calculationmeans”. The calculation means may optionally be engaged by activationmeans operable by an individual. The activation means may possess atleast one position enabling the secondary automatic control system 57 tobe made active. Thus, the secondary automatic control system 57 may beinhibited in certain situations, e.g. while the aircraft is notoverflying a liquid surface.

The secondary automatic control system 57 and/or the secondary controlmember 56 are configured to deploy the secondary floats after ditching.

Reference may be made of the state of the art to find embodiments ofinflaters and control systems for those inflaters in order to deploy thesecondary floats after ditching.

In the second embodiment of FIG. 2, no inflater is provided for directlyinflating the secondary floats 30, i.e. without passing via a main float25.

In this second embodiment, at least one main inflater 51 is thusconnected by a pipe to at least one main float 25, each main float 25being connected by a pipe to at least one main inflater 51.

Furthermore, each secondary float 30 is connected to a main float 25 viaa valve 65. For example, each secondary float 30 is connected to asingle main float 25 via a valve, and each main float 25 is connected toa secondary float 30 via such a valve.

A valve 65 thus acts as an interface between a main inside volume of amain float and a secondary inside volume of a secondary float. When thevalve is opened, some of the fluid contained in the main float fills thesecondary float until an equilibrium position is reached. Onequilibrium, the main float and the secondary float are both inflated.Where necessary, it is possible at this stage to top up the volume offluid by acting on an inflater.

The valve 65 may be a passive valve that opens when the pressure thatexists in the main inside volume exceeds a pressure threshold. Thepassive valve may be designed so that the threshold is reached when themain float is subjected to forces during ditching, or on activating aninflater, where appropriate.

Alternatively, the valve 65 may be an electromechanically activatedvalve that opens on an order from a processor unit 60. The processorunit may determine whether predetermined inflation conditions aresatisfied, and it may activate the valve 65 in order to inflate thesecondary floats 30.

The processor unit may be in the form of selector means operable by aperson so as to enable an order to be transmitted to the calculationmeans to inflate the main floats and/or the secondary floats. The term“selector means” may designate a button, a touch screen, voice controlmeans, a keypad, or a pointer for operating computer means, . . . .

The processor unit 60 may also be in the form of calculator connected tosensors. For example, at least one immersion sensor may serve to detectthe presence of water, and where applicable it transmits an order to theprocessor unit to inflate the secondary floats 30.

By way of example, the processor unit may process a processor, anintegrated circuit, a programmable system, a logic circuit, theseexamples not limiting the scope to be given to the term “processorunit”.

FIGS. 1, 3, and 4 serve to illustrate the method performed by theinvention.

With reference to FIG. 1, the main floats 25 and the secondary floats 30are folded in flight under normal conditions.

With reference to FIG. 3, when ditching is imminent, all of the mainfloats 25 are deployed, either on order from a pilot or else on orderfrom calculation means.

With reference to FIG. 4, after ditching, the aircraft is to be found ona liquid surface. All of the secondary floats 30 are deployed, either onorder of a pilot, or else on order of calculation means or of aprocessor unit.

FIG. 4 shows the fact that by arranging a main float 25 between asecondary float 30 and the airframe 2, a large spread 200 may extendtransversely between two secondary floats 30. This characteristic canoptimize the floating stability of the aircraft.

FIG. 5 shows an aircraft having main floats 25 and secondary floats 30that are deployed.

This aircraft presents a pair 39 of front float units comprising a leftfront float unit 37 and a right front float unit 38.

In addition, the aircraft has a pair 42 of rear float units comprising aleft rear float unit 41 and a right rear float unit 40.

Furthermore, FIG. 5 shows in dashed lines the configuration of prior artfloats. FIG. 5 thus shows that a float unit can be arranged to take theplace of such a prior art float, and can present substantiallyequivalent overall size.

Naturally, the present invention may be subjected to numerous variationsas to its implementation. Although several embodiments are described, itwill readily be understood that it is not conceivable to identifyexhaustively all possible implementations. It is naturally possible toenvisage replacing any of the means described by equivalent meanswithout going beyond the ambit of the present invention.

What is claimed is:
 1. A buoyancy method for deploying a plurality offloats of a buoyancy system of an aircraft, wherein the plurality offloats comprises a plurality of main floats and a plurality of secondaryfloats, the main floats and the secondary floats being folded in flightand being for deploying outside an airframe of the aircraft in order tostabilize the aircraft on a liquid surface, the method comprising thefollowing steps: deploying the main floats in flight prior to ditching;and deploying the secondary floats after ditching.
 2. The methodaccording to claim 1, wherein the method includes a step of pairing thefloats, the plurality of floats comprising at least one pair of mainfloats and at least one pair of secondary floats, each of the at leastone pair of main floats comprising two main floats arranged transverselyon either side of the airframe, and each of the at least one pair ofsecondary floats comprising two secondary floats arranged transverselyon either side of the airframe.
 3. The method according to claim 1,wherein the method includes a step of forming a plurality of floatunits, each float unit comprising a single main float and a singlesecondary float arranged side by side, each main float of a float unitbeing arranged transversely between the secondary float of the floatunit and the airframe.
 4. An aircraft having a buoyancy system, thebuoyancy system comprising a plurality of floats, each float of theplurality of floats being folded in flight other than during a stage ofditching, the buoyancy system including a deployment system fordeploying each float of the plurality of floats outside an airframe ofthe aircraft, the plurality of floats comprising a plurality of mainfloats and a plurality of secondary floats, wherein the buoyancy systemis configured to deploy the main floats outside the airframe in flightprior to ditching and to deploy the secondary floats outside theairframe after ditching.
 5. The aircraft according to claim 4, whereinthe plurality of floats forms a plurality of float units, each floatunit having a single main float and a single secondary float arrangedside by side, a main float of a float unit being arranged transverselybetween the secondary float of the float unit and the airframe.
 6. Theaircraft according to claim 5, wherein the plurality of float unitscomprises at least one pair of float units, the at least one pair offloat units comprising two float units arranged transversely on eitherside of the airframe.
 7. The aircraft according to claim 6, wherein thetwo float units of a pair of float units are arranged symmetrically oneither side of the airframe.
 8. The aircraft according to claim 4,wherein each main float is connected to the airframe by at least onemain cord.
 9. The aircraft according to claim 4, wherein each secondaryfloat is connected to the airframe by at least one secondary cord. 10.The aircraft according to claim 4, wherein a secondary float and a mainfloat have a partition in common.
 11. The aircraft according to claim 4,wherein a secondary float is stitched and/or adhesively bonded to a mainfloat.
 12. The aircraft according to claim 4, wherein the deploymentsystem comprises at least one main inflater in fluid flow communicationwith only at least one main float to inflate only the at least one mainfloat, the deployment system including at least one secondary inflaterin fluid flow communication with only at least one secondary float inorder to inflate only the at least one secondary float.
 13. The aircraftaccording to claim 4, wherein each secondary float is in fluid flowcommunication with at least one main float via a valve, the deploymentsystem comprising at least one main inflater in fluid flow communicationwith only the main floats in order to inject a fluid only into the mainfloats, no inflater directly feeding any secondary float with fluid. 14.The aircraft according to claim 13, wherein the valve is a passivevalve, the passive valve opening when pressure existing in the mainfloat provided with the passive valve exceeds a threshold, the pressurebeing less than the threshold prior to ditching.
 15. The aircraftaccording to claim 13, wherein the aircraft includes a processor unit,the valve is an active valve, the active valve is connected to theprocessor unit, and the active valve is controlled by the processorunit.